The present invention relates generally to container ends and more particularly to an improved fully open end.
Containers having easy open ends have become well-known in recent years and now enjoy a considerable measure of consumer acceptability. One type of easy open end is a full open end closure that normally includes an end panel that is permanently secured to one end of a container body by a permanent seam and has a weakened score line adjacent the permanent connection to define a removable section. An opening tab is secured to a portion of the removable section, normally through an integral rivet forming part of the removable section. Containers having full open ends are used for packaging various types of products, such as coffee, nuts, candy and foods containing liquid.
To separate the removable section from the permanently secured section, the opening tab is moved along a path by initially pivoting the tab towards the permanent seam to cause a downward movement of the portion of the removal section between the rivet and the score line to produce initiate rupture of the score line or weakened area. Subsequently, the tab is pulled in an opposite direction along a path away from the initially ruptured section until the entire score line has been ruptured and the removable section is detached from the permanent section.
As is explained in the above application, one difficulty encountered in full open end closures is that the severed edge of the removable section tends to become located under the adjacent edge of the permanently secured section during initial rupture of a portion of the weakened area of the score line, making it extremely difficult, if not impossible, to remove the entire closure.
In the co-pending application, it is explained that this is believed to be in part caused by loose metal in the removable section resulting from the scoring operation which forms the score line or weakened area that defines the removable portion of the end. This problem has been at least partially solved by providing a trough adjacent the rivet as well as a circumscribing bead located adjacent the weakened area to take up excess metal that is produced in the removable section during the formation of the finished end shown in the above application. As explained therein, the trough and circumferential bead also provides the advantage of preventing crowning between opposite edges of the removable section while it is being separated from the permanent section.
A further problem is that the normal scoring operation results in considerable stress concentration in the metal in the score line or frangible connection and often produces a small crack in the weakened area which thereby may result in fracture of the weakened area before it is desired.
In the normal scoring operation, the score line is produced by supporting one surface of the panel on a flat support and forcing a truncated V-shaped scoring member into the opposite surface of the panel. During the scoring operation, the metal that is located below the flat portion of the truncated V-shaped scoring member is displaced substantially normal to the panel and results in the large stress concentration in the weakened area of the score line. It has been found that such a scoring operation normally results in at least a small crack adjacent either corner or edge of the reduced cross-section or weakened area which will enhance the possibility of fracture of the weakened area before desired. Stated another way, the portion of the metal directly below the flat surface of the scoring element will act as a slug that initially consists of a section of metal in the panel that has a thickness equal to the thickness of the panel and is reduced in thickness to that of the ultimate thickness of the weakened area.
The problem of producing a small crack or fracture in the weakened area of the removable end is particularly acute when utilizing a metal such as tin plate for the end. Normally, such metals must be surface coated on both surfaces of the panel to prevent the bare metal from being exposed to either the contents of the container or the surrounding atmosphere. When utilizing a scoring operation of the type described above, one or both surface coatings may be cracked or fractured during the scoring operation.
Another problem in the use of full open end closures has come to light when using containers with these types of closures for packaging certain products that are packaged at conditions other than atmospheric pressure. It has been found that when certain products, such as coffee, are packaged in containers of the type discussed above, the initial rupture of the score line will result in an immediate equalization of the pressure between the inside and outside of the container, which many times results in the product being forced from the container through the initially ruptured area of the score line.